From Apprentice To Artisan 翻译 16

Stella981
• 阅读 467

上一篇

Single Responsibility Principle 单一职责原则

Introduction 介绍

The "SOLID" design principles, articulated by Robert "Uncle Bob" Martin, are five principles that provide a good foundation for sound application design. The five principles are:

罗伯特“鲍勃叔叔”马丁阐述了名为“坚实”的一些设计原则(译者注:看下面五个原则的首字母正是 SOLID)。这些都是制作完善的程序设计的优秀基础,一共有五个原则:

  • The Single Responsibility Principle 单一职责原则
  • The Open Closed Principle 开放封闭原则
  • The Liskov Substitution Principle 里氏替换原则
  • The Interface Segregation Principle 接口隔离原则
  • The Dependency Inversion Principle 依赖反转原则

Let's explore each of these principles in more depth, and look at some code examples illustrating each principle. As we will see, each principle compliments the others, and if one principle falls, most, if not all, of the others do as well.

让我们深入探索一下,再看点代码样例来说明各个原则。我们将看到,每个原则之间都有联系。如果其中一个原则没有被遵循,那么其他大部分(可能不会是全部)的原则也会出问题。

In Action 实践

The Single Responsibility Principle states that a class should have one, and only one, reason to change. In other words, a class' scope and responsibility should be narrowly focused. As we have said before, ignorance is bliss when it comes to class responsibilities. A class should do its job, and should not be affected by changes to any of its dependencies.

单一职责原则规定一个类有且仅有一个理由使其改变。换句话说,一个类的功能边界和职责应当是十分狭窄且集中的。我们之前就提到过,在类的职责问题上,无知是福。一个类应当做它该做的事儿,并且不应当被它的依赖的任何变化所影响到。

Consider the following class:

考虑下列类:

<!-- lang: php -->
class OrderProcessor {
    public function __construct(BillerInterface $biller)
    {
        $this->biller = $biller;
    }
    public function process(Order $order)
    {
        $recent = $this->getRecentOrderCount($order);
        if($recent > 0)
        {
            throw new Exception('Duplicate order likely.');
        }
        
        $this->biller->bill($order->account->id, $order->amount);
        
        DB::table('orders')->insert(array(
            'account'    =>    $order->account->id,
            'amount'    =>    $order->amount,
            'created_at'=>    Carbon::now()
        ));
    }
    protected function getRecentOrderCount(Order $order)
    {
        $timestamp = Carbon::now()->subMinutes(5);
        return DB::table('orders')->where('account', $order->account->id)
                                                ->where('created_at', '>=', $timestamps)
                                                ->count();
    }
}

What are the responsibilities of the class above? Obviously, its name implies that it is responsible for processing orders. But, based on the getRecentOrderCount method, we can also see that it is responsible for examining an account's order history in the database in order to detect duplicated orders. This extra validation responsibility means that we must change our order processor when our data store changes, as well as when our order validation rules change.

上面这个类的职责是什么?很显然顾名思义,它是用来处理订单的。不过由于getRecentOrderCount这个方法的存在,这个类就有了在数据库中审查某帐号订单历史来看有没有重复订单的职责。这个额外的验证职责意味着当我们的存储方式改变或当订单验证规则改变时,我们的这个订单处理器也要跟着改变。

We should extract this responsibility into another class, such as an OrderRepository:

我们必须将这个职责抽离出来放到另外的类里面,比如放到OrderRepository

<!-- lang:php -->
class OrderRepository {
    public function getRecentOrderCount(Account $account)
    {
        $timestamp = Carbon::now()->subMinutes(5);
        return DB::table('orders')->where('account', $account->id)
                                                ->where('created_at', '>=', $timestamp)
                                                ->count();
    }

    public function logOrder(Order $order)
    {
        DB::table('orders')->insert(array(
            'account'    =>    $order->account->id,
            'amount'    =>    $order->amount,
            'created_at'=>    Carbon::now()
        ));
    }
}

Then, we can inject our repository into the OrderProcessor, alleviating it of the responsibility of researching an account's order history:

然后我们可以将我们的资料库(译者注:OrderRepository )注入到OrderProcessor里,帮后者承担起对账户订单历史的处理责任:

<!-- lang:php -->
class OrderProcessor {
    public function __construct(BillerInterface $biller, OrderRepository $orders)
    {
        $this->biller = $biller;
        $this->orders = $orders;
    }

    public function process(Order $order)
    {
        $recent = $this->orders->getRecentOrderCount($order->account);

        if($recent > 0)
        {
            throw new Exception('Duplicate order likely.');
        }

        $this->biller->bill($order->account->id, $order->amount);

        $this->orders->logOrder($order);
    }
}

Now that we have abstracted our order data gathering responsibilities, we no longer have to change our OrderProcessor when the method of retrieving and logging orders changes. Our class responsibilities are more focused and narrow, providing for cleaner, more expressive code, and a more maintainable application.

现在我们提取出了收集订单数据的责任,当读取和写入订单的方式改变时,我们不再需要修改OrderProcessor这个类了。我们的类的职责更加的专注和精确,这提供了一个更干净、更有表现力的代码,同时也是更容易维护的代码。

Keep in mind, the Single Responsibility Principle isn't just about less line of code, it's about writing classes that have a narrow responsibility, and a cohesive set of available methods, so make sure that all of the methods in a class are aligned with the overall responsibility of that class. After building a library of small, clear classes with well defined responsibilities, our code will be more decoupled, easier to test, and friendlier to change.

请记住,单一职责原则的关键不仅仅是让函数变短,而是写出职责更精确更高内聚的类,所以要确保类里面所有的方法都属于该类的职责之下的。在建立一个小巧、清晰且职责明确的类库以后,我们的代码会更加解耦,更容易测试,并且更易于更改。

下一篇

点赞
收藏
评论区
推荐文章
blmius blmius
2年前
MySQL:[Err] 1292 - Incorrect datetime value: ‘0000-00-00 00:00:00‘ for column ‘CREATE_TIME‘ at row 1
文章目录问题用navicat导入数据时,报错:原因这是因为当前的MySQL不支持datetime为0的情况。解决修改sql\mode:sql\mode:SQLMode定义了MySQL应支持的SQL语法、数据校验等,这样可以更容易地在不同的环境中使用MySQL。全局s
Jacquelyn38 Jacquelyn38
2年前
2020年前端实用代码段,为你的工作保驾护航
有空的时候,自己总结了几个代码段,在开发中也经常使用,谢谢。1、使用解构获取json数据let jsonData  id: 1,status: "OK",data: 'a', 'b';let  id, status, data: number   jsonData;console.log(id, status, number )
皕杰报表之UUID
​在我们用皕杰报表工具设计填报报表时,如何在新增行里自动增加id呢?能新增整数排序id吗?目前可以在新增行里自动增加id,但只能用uuid函数增加UUID编码,不能新增整数排序id。uuid函数说明:获取一个UUID,可以在填报表中用来创建数据ID语法:uuid()或uuid(sep)参数说明:sep布尔值,生成的uuid中是否包含分隔符'',缺省为
Stella981 Stella981
2年前
KVM调整cpu和内存
一.修改kvm虚拟机的配置1、virsheditcentos7找到“memory”和“vcpu”标签,将<namecentos7</name<uuid2220a6d1a36a4fbb8523e078b3dfe795</uuid
Easter79 Easter79
2年前
Twitter的分布式自增ID算法snowflake (Java版)
概述分布式系统中,有一些需要使用全局唯一ID的场景,这种时候为了防止ID冲突可以使用36位的UUID,但是UUID有一些缺点,首先他相对比较长,另外UUID一般是无序的。有些时候我们希望能使用一种简单一些的ID,并且希望ID能够按照时间有序生成。而twitter的snowflake解决了这种需求,最初Twitter把存储系统从MySQL迁移
Wesley13 Wesley13
2年前
mysql设置时区
mysql设置时区mysql\_query("SETtime\_zone'8:00'")ordie('时区设置失败,请联系管理员!');中国在东8区所以加8方法二:selectcount(user\_id)asdevice,CONVERT\_TZ(FROM\_UNIXTIME(reg\_time),'08:00','0
Wesley13 Wesley13
2年前
00:Java简单了解
浅谈Java之概述Java是SUN(StanfordUniversityNetwork),斯坦福大学网络公司)1995年推出的一门高级编程语言。Java是一种面向Internet的编程语言。随着Java技术在web方面的不断成熟,已经成为Web应用程序的首选开发语言。Java是简单易学,完全面向对象,安全可靠,与平台无关的编程语言。
Stella981 Stella981
2年前
Django中Admin中的一些参数配置
设置在列表中显示的字段,id为django模型默认的主键list_display('id','name','sex','profession','email','qq','phone','status','create_time')设置在列表可编辑字段list_editable
Wesley13 Wesley13
2年前
MySQL部分从库上面因为大量的临时表tmp_table造成慢查询
背景描述Time:20190124T00:08:14.70572408:00User@Host:@Id:Schema:sentrymetaLast_errno:0Killed:0Query_time:0.315758Lock_
Python进阶者 Python进阶者
2个月前
Excel中这日期老是出来00:00:00,怎么用Pandas把这个去除
大家好,我是皮皮。一、前言前几天在Python白银交流群【上海新年人】问了一个Pandas数据筛选的问题。问题如下:这日期老是出来00:00:00,怎么把这个去除。二、实现过程后来【论草莓如何成为冻干莓】给了一个思路和代码如下:pd.toexcel之前把这